1. Field of the Invention
This invention relates generally to automatically operable valves, and is more particularly concerned with a valve that is automatically closable on occurrence of a seismic event of a predetermined severity, and manually closable as desired.
2. Discussion of the Prior Art
In areas of the world in which earthquakes, or seisms, are reasonably expectable there is concern for collateral damage flowing from the seism. By way of example, even though a relatively slight amount of damage may be caused to a structure, it is possible that a gas line will be broken, and major damage may be caused by a gas explosion. Similarly, toxic or otherwise hazardous gases may be released into the atmosphere. In an effort to prevent collateral damage, there have been automatically operable valves and the like to terminate the flow of gas or other fluids early in the occurrence of the seismic event.
The prior art valves have generally been rather complex mechanically, frequently including one or more linkages that must be operated to open or close the valve. Other valves may be somewhat simpler, but none of the prior art valves is easily variable so that severity of the seism required to operate the valve can be changed at will. One exception to the last statement is the U.S. Pat. No. 5,115,829 to Franzke. This patent discloses a rather simple automatically operable valve, the sensitivity of which is relatively easy to change. However, the Franzke patent is somewhat crudely done, with a housing fabricated from sheet stock, and the device does not lend itself to mass manufacture or efficient operation. Also, there is no provision for activation of the valve manually, to close the valve when desired.